Well depending on exactly what part of the UK you are in, and if the average temperatures I was looking at are correct your going to to want to go with a early blooming, mold, and cold resistant plant. You may want to look at some of the auto flowering varieties possibly by Greenthumb http://drgreenthumb.com/GreenthumbSeedsProfiles.htm these will start and finish in a matter of about a month and a half so if you get a month or so of 70(f) and up you could get a crop. The Iranian variety he has looks to be a hardy plant from some of the reviews I have read. The problem is how cold most places in the UK are coupled with the over average (what we have here in the states at least) rainfall, which together makes a bit a problem for growing any sort of late blooming strains, unless a Ruderalis cross. If you went the green house route with small to medium sized pots possible inside other pots insulated with something you could possible pull some other strains that are larger producers (I hear Northern lights can stand "some" cold), possible no promises.
Not sure about growing inUK weather but Northern Lights are extremely easy to grow. Very resistant to all types of stress- insects, temps, lack of nutes, physical abuse, and just simple neglect.